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EH 7591 Opinions?

BuzzK

BuzzK

AK Member
Subscriber
NOS, good old Westinghouse 7591s (made in Elmira Heights, NY) are very hard to come by, and pretty pricey if you can find them.

I'm restoring a Kenwood 1100u which requires a quad of them. I'm not sure I want to deplete my meager stock of USA tubes for this particular project.

I'm familiar with the Sovtek 7591XYZ (basically repinned 5881s or equiv.) and am not a fan. I've used the big bottle EH 7591s and thought they were OK.

I'm interested in opinions on the sonics -- and particularly the longevity and quality -- of the Electro Harmonix product.

Thanks in advance,

BuzzK
 
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Since that Kenwood never came with Westinghouse tubes, probably ones that were of Japanese manufacture, why sweat it? I'm sure the EH will do fine.
 
I've been satisfied with the EHs. Here's a list of what I've tried.
Westinghouse
Sylvania
GE (maybe Sylvies?)
Hitachi
JJ
EH

Sonic rankings:
1. Westinghouse
2. EH
3. the also rans.

As far as robustness, I suspect that if they're not pushed hard like many Westies were for years, they should last. Many suggest using a 220k grid resistor instead of the 300k+ some manufacturers used during the wattage wars.
Use a reliable seller. I've found cathode current to be inconsistent from tube to tube, but not from turn-on to used for hours.
 
I've been perfectly happy with the EH7591 tubes in my Fisher 800c. Just make sure that you aren't running them too hot.

-Derek
 
The EH is a good tube. Richer and less tizzy than the JJ version. Not quite as articulate as a Westie or Sylvania in the middle, but close enough. If you didn't have those on hand, you wouldn't likely notice the difference otherwise.

All the ones I have used have held up just fine in the field (some are getting close to a decade old), and I don't do the 220kohm Fisher mod with them.

If you can't afford the old production, the EH will satisfy just fine.

Just make sure they fit. Can't stand the fat envelopes.
 
This might start a war but as a 7591 user and the stuff now available what about a socket rewire and use 6L6 tubes instead? You would loose a little power but the sound should still be as nice. any thoughts??
 
I've had really good luck with the EH 7591's. I did the grid resistor mod on my Fisher X-101-B just to make life easy on the 7591's. I think they EH tubes sound nice and the price is right. I don't like the EH fat/tall bottles. They can make for a mighty tight fit.
 
I have had a set of EH 7591's in my MC 225 Macintosh power amp since they first came out, what about 10 years ago...have worked flawlessly since then. I can't tell the difference between these and NOS ones..in sound.
 
Personally, at least in Fisher 500s and some Scott amps, I think the EH 7591s sounded BETTER than OEM tubes. I tested back-to-back a set of four NOS Sylvania 7591s with EH7591s... the EH had more "headroom" (max power on transients) and better bass dynamics, in a Scott 208 amp...

And, with their large plates, they're harder to burn up than NOS tubes. Get them biased right (220K or so grid resistors, NOT the 300K+ that many manufacturers used), and they're brick reliable, IME.

Regards,
Gordon.
 
In fixed bias amplifiers of typically 30-35 watts per channel, the EH tube will provide typically 90% or better of NOS power and distortion performance, where as the JJ tube will not come even close in that setting, usually putting out barely 70% of NOS power output. Therefore, the EH tube is a very workable modern day replacement for the original tube -- as long as it will physically fit. Also, 6L6 class tubes are very capable of putting out every bit as much power as any 7591 tube or design, but will require additional drive and modified screen voltages to produce the same performance as that of the original 7591 design.

Dave
 
I measured greater output before clipping (higher voltage into a dummy load) with the EH7591s in the Scott 208, than with the NOS Sylvania 7591s. And this was after biasing both sets correctly (around 32ma per tube)...

The NOS 7591s were verified as in new condition, on both Hickok TV7A and Sencore Mighty Mite 5 tube testers...

Regards,
Gordon.
 
I've got a set on my SANSUI 1000A. It has the "Animal Trap" retainers on it which I am leery of when using the EH's due to the "coin base". It had a mixed set fo Westy's and Toshiba's. The Toshiba's are weak but the Westy's are just plain wore out. I picked up a set of EICO branded Westy's and they sound just ok, compared to the EH's. The EH's have a lot more punch, transients are cleaner, bass is tighter. I'm gonna remove the "Animal traps" and just go for it on the EH's.

The JJ's I got were a friggin nightmare. 3 of 4 died within 3 weeks, and the 4th redplated within 2 hours of starting. The unit is totally recapped, 200K grid resistors, Bias set to spec(single bias pot version modded to 4 pot version), and is running on a bucking transformer @ 115V. So no real excuse for the JJ's to go like they did other than piss poor quality! Got almost 300 hours on the EH's and they act like they want more power all the time. Kinda like having a 383 stroker in a VEGA and pussyfooting the throttle. Guess it's time to cut them loose.

Larry
 
Larry,
How do those EH's fit next to the Sansui transformers? I would think the larger size would create heat issues in that unit. I also have a 1000a and skipped over the EH tubes because of size. Maybe I should reconsider them.
Thanks,
Dave
 
Dave C said:
Larry,
How do those EH's fit next to the Sansui transformers? I would think the larger size would create heat issues in that unit. I also have a 1000a and skipped over the EH tubes because of size. Maybe I should reconsider them.
Thanks,
Dave
Click to expand...

Maybe related: I have a Scott LK-72A and the 4 Daystroms will hit their end of life in a near future (testing around 75% on my Jackson 648).

I bought a spare set of EH's after seeing a similar LK-72A fitted with them (my tech at the moment recommended me the JJ's but their life decreased significantly in just one year of constant use... It's why I suck the remaining life of the Daystrom's). The tubes are touching the OPT's on the pictures I saw. I think this Scott was owned by the AK member Bricktop.

I'm also a bit hesitant to use them fearing the OPT's (or the tubes themselves) could be damaged by such heat...

http://picasaweb.google.co.jp/Gregory.Micah/ScottLK72#
 
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Dave C said:
Larry,
How do those EH's fit next to the Sansui transformers? I would think the larger size would create heat issues in that unit. I also have a 1000a and skipped over the EH tubes because of size. Maybe I should reconsider them.
Thanks,
Dave
Click to expand...

They are a "couple of RCH's" tighter than the originals. and They actually run cooler than the original Toshiba's and the EICO's at the same settings. I've noticed that the 6K/600 oHm resistor(s) are hotter than the tubes.

You can do a couple of things if you are worried about the heat output and proximity of the new tubes. This is especially relevant in a unit such as the SANSUI 1000A and I would suspect most Scott's due to their Form Factor.

1.) Bias them on the cool side.
2.) Get some self adhesive metal foil and attach to the sides of the PTx and the OPTx so the heat tends to reflect back to the tubes.
3.) Force ventilate. You want to PULL the air across the tube not push it.
Fans on top, 1 per pair of tubes, slightly forward of them to get the air moving across the tubes, TX's, and the resistors, and help move the heat away from the tubes. I line mine up with the CAN CAPS.

Needless to say, but I will anyway! DO NOT STACK the 1000A. Natural Convection on this unit is marginal at best, fans Help a lot, and blocking the airflow is tantamount to torching the unit.


With the old tubes I was forced to employ #'s 1 & 3, even after biasing on the cool side(25ma). After Biasing on the cool side(25-26ma and they still sound good) with the new tubes, I've only had to stick with #1. MARK2WAE has the full up mod (1 thru 3) but I suspect that he is running them wide open.

The above IMO. YMMV.

Larry
 
larryderouin said:
They are a "couple of RCH's" tighter than the originals. and They actually run cooler than the original Toshiba's and the EICO's at the same settings. I've noticed that the 6K/600 oHm resistor(s) are hotter than the tubes.

You can do a couple of things if you are worried about the heat output and proximity of the new tubes. This is especially relevant in a unit such as the SANSUI 1000A and I would suspect most Scott's due to their Form Factor.

1.) Bias them on the cool side.
2.) Get some self adhesive metal foil and attach to the sides of the PTx and the OPTx so the heat tends to reflect back to the tubes.
3.) Force ventilate. You want to PULL the air across the tube not push it.
Fans on top, 1 per pair of tubes, slightly forward of them to get the air moving across the tubes, TX's, and the resistors, and help move the heat away from the tubes. I line mine up with the CAN CAPS.

Needless to say, but I will anyway! DO NOT STACK the 1000A. Natural Convection on this unit is marginal at best, fans Help a lot, and blocking the airflow is tantamount to torching the unit.


With the old tubes I was forced to employ #'s 1 & 3, even after biasing on the cool side(25ma). After Biasing on the cool side(25-26ma and they still sound good) with the new tubes, I've only had to stick with #1. MARK2WAE has the full up mod (1 thru 3) but I suspect that he is running them wide open.

The above IMO. YMMV.

Larry
Click to expand...

Is 25-26ma not too cold for 7591's?
 
gugusse said:
The tubes are touching the OPT's on the pictures I saw. I think this Scott was owned by the AK member Bricktop.

I'm also a bit hesitant to use them fearing the OPT's (or the tubes themselves) could be damaged by such heat...

http://picasaweb.google.co.jp/Gregory.Micah/ScottLK72#
Click to expand...

That's a no-no in my opinion. The envelope's heat load easily conducts into anything it touches. While ok for a tube shield or a tweak specifically designed for the heat, an OPT is not designed as a heat sink.

In the pix, those outputs are also a little too close to the filters in my opinion.

I hear you about the JJs. They don't knock one over . . . except when they occasionally fail.

This is the one bugaboo of an otherwise excellent new production output - the EH is too FAT (and too tall, too) for some of the vintage layouts.

In this particular situation, I would bite the bullet and hunt down old production. There are still decent used examples still out there, but be prepared to pay, especially for quads. Westinghouses and Sylvanias are sonically close enough that you could mix pairs in an absolute worst case. And bias them on the cool end.
 
sgmlaw said:
That's a no-no in my opinion. The envelope's heat load easily conducts into anything it touches. While ok for a tube shield or a tweak specifically designed for the heat, an OPT is not designed as a heat sink.

In the pix, those outputs are also a little too close to the filters in my opinion.

I hear you about the JJs. They don't knock one over . . . except when they occasionally fail.

This is the one bugaboo of an otherwise excellent new production output - the EH is too FAT (and too tall, too) for some of the vintage layouts.

In this particular situation, I would bite the bullet and hunt down old production. There are still decent used examples still out there, but be prepared to pay, especially for quads. Westinghouses and Sylvanias are sonically close enough that you could mix pairs in an absolute worst case. And bias them on the cool end.
Click to expand...

Ok,

I have three unused spare ones: 2 RCA's and one GE. There's also two Sylvania's presently on my Heathkit AA-100 testing good.

I'll probably find a way to get a working quad out of these 5 tubes. I'll keep the EH's to put on the AA-100 instead (space is not a concern there).

For now, the weakening Daystrom's do the job as the sonics doesn't seem to suffer (as long as the sound doesn't deteriorate too much, I'll use them...).

Thanks.

Patrice
 
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